Chin Up Protocol question (rest periods)

[BenpMelton]

Hello - Sorry to post another thread about this topic, I've searched many of them and can't find an answer to this simple question:

How long should the rest periods be between these "submaximal" sets of chins? I did my first round today, and did sets of 5 with about a 1 minute rest in between. When that got too hard I lowered down to sets of 3-4 with 45-60 seconds in between. I did 35 chinups total. Is there something I could be doing differently here?

[Mark Rippetoe]

I walk a lap to time my rest. Figure out a 2-minute lap and use that.